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While running an Ubuntu kernel (not a mainline or third-party kernel)
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apport-collect 2038685
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This change has been made by an automated script, maintained by the
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** Changed in: linux (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/2038685
Title:
Missing BTF file in Ubuntu ESM kernels
Status in linux package in Ubuntu:
Incomplete
Bug description:
This is a follow-up from: https://discourse.ubuntu.com/t/ask-us-
anything-about-ubuntu-kernels/27664/142
Older Ubuntu distributions come with a kernel image that support eBPF
but are not built with a BTF file published (/sys/kernel/btf/vmlinux).
This BTF file is crucial when trying to run eBPF programs that were
built with CO-RE in mind such that a program can be compiled once and
run in any kernel (with some caveats) because the BPF loaders can use
the BTF file to relocate addresses of kernel fields at load time for
the currently running kernel. In the past I've used the debug symbols
that Ubuntu publishes to create BTF files using `pahole` for these
older kernels and then re-using that BTF file for any machine running
that kernel. This is not ideal but I had managed to work around it.
However, on distributions that are under ESM (Ubuntu 16 + Ubuntu 18)
there isn't a debug symbols repository from where to pull the debug
symbols packages to build their respective BTF file and no BTF file is
generated when the kernel is built. This essentially makes these ESM
kernels incompatible with eBPF programs that run using CO-RE (which is
more or less the norm nowadays). Based on my conversation on the
discourse link above it seems like ideally these ESM kernels should be
published with a BTF file.
P.S. I wasn't able to submit this through `ubuntu-bug linux` as it
gave me an error saying `Problem in linux-image-5.4.0-164-generic This
is not an official Ubuntu package. Please remove any third party
package and try again`. I am not sure why it says that as this is a
Ubuntu VM downloaded from the Ubuntu site, upgraded by doing `pro
attach` and then updated to the latest ESM kernel.
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